DESCRIPTION: (Applicant's Description) Numerous studies have investigated the association of diet and breast cancer risk. However, the results of previous research have been inconsistent. Many dietary studies have been limited by being conducted in populations of relative "dietary affluence" (i.e. high-fat, high-meat, low-fiber). In such populations, a comparison of high-consuming half to low-consuming half may not be sufficient to reveal any non-linear associations. By conducting a dietary study in Shanghai it will be possible to evaluate different levels of dietary intake, including lower fat consumption and higher fiber and soy (phytoestrogens) consumption. In addition, due to the quickly shifting socioeconomic climate in China, the proposed study will provide a chance to evaluate the impact of changing dietary habits on breast cancer risk. The proposed study will also have the unique opportunity to compare dietary intake with breast cancer risk on a cellular and hormonal level, using breast tissue cell proliferation, cell apoptosis, and serum hormone concentrations. Finally, the results of the proposed study will be combined with those of several studies from the early and mid-1980's to develop a time-trend analysis of diet and increasing breast cancer incidence in Shanghai. This use of aggregate data may provide further insight into associations which have been unclear in traditional case-control studies. The study population will consist of approximately 856 cases and 856 matched controls who are currently enrolled in a randomized trial of breast self-examination, or a nested case-control study of breast cell proliferation. Dietary data and a l0 ml blood specimen will be gathered from the women. The proposed study is unique in that it approaches the question of diet and breast cancer risk in three different ways; 1) food and nutrient associations with breast cancer, 2) food and nutrient associations with cell kinetics; and 3) diet and breast cancer time-trend analyses. If an association is seen between dietary factors and breast cancer risk, it may provide insight into the frustratingly inconsistent results of previous dietary studies and will be of relevance to women in Shanghai and worldwide. An important advantage of this study is that it will utilize a very large, accessible, and relatively stable female population currently under study. Our study will yield timely, new and cost-efficient results with high statistical power.